The manufacture of printed circuits uses photographic processes to make the tracks or pattern of the circuit on a base board, which consists of one or more layers of copper or other conductive materials.
For this purpose a layer of material sensitive to ultraviolet light, for example, is spread on the board; that layer is photographically exposed, and the board is then introduced into baths that dissolve the unexposed layer and the underlying layer made of conductive material to produce the circuit tracks.
These known procedures comprise various stages including the stage when the said sensitive layer is fired, during which the boards that constitute the circuit base are introduced into a kiln, usually the tunnel type, in which the coating layer is "fired".
At present, hooking devices are used for this purpose which allow the printed circuits to be picked up from feeder cars and introduced onto a conveyor line situated in the upper inner part of a tunnel kiln; finally the treated circuits are unloaded into a car situated at the tunnel outlet.
These known hooking devices comprise a pair of jaws, fitted to slide along lateral guides which allow synchronised movement in relation to the circuit feed area, so that by moving alternately back and forth they can grip the circuit at the sides and handle it for the purpose of the functions described above.
The main drawback of these known hooking devices is that the measurements of the circuit board need to be taken every time, and the jaw movements adapted to suit them.
In many known units the movement to be effected by the jaws is measured by optical sensors, which detect the width of the circuit and send the data detected to control devices which accordingly set the extent of the travel to be performed by the jaws so that they hook onto the two opposite sides of each printed circuit with precision.
All this obviously involves high costs for both the manufacture and the running of the plant, which have a considerable influence on the price of the finished product.